I've just found this emulator and couldn't be more excited. I've tried it with my copy of Smash Bros and it runs, at around 80% speed. I've posted a link to my Mac specs further down and was hoping someone could advise me if that's the best I'm going to get or if I should be able to tweak it further. I'm only interested in running GC games.

Ah, many apologies for that. I guess for a start I'd be happy getting Smash Bros running at GC quality, so not HD. Then if I know it's possible I'd be happy to spend many an hour trying everything out myself.